A highwall mining system has recently been developed by Mining Technologies, Inc. and is generally described in, for example, U.S. Pat. Nos. 5,112,111 and 5,261,729 to Addington et al. Highwall mining is particularly useful where the coal seam is located at a significant depth below the surface and the amount of overburden that must be removed to reach the coal makes further strip mining economically unfeasible.
The highwall mining system includes a miner or mining machine for cutting material from the seam and a conveyor for conveying the won aggregate material from the mining machine for recovery. The conveyor is formed by a series of individual conveyor units that are coupled or interconnected in series so as to form a train. The last unit of the conveyor train is supported on a launch vehicle anchored to the bench outside the mine seam. The launch vehicle includes an underlying belly conveyor that receives aggregate material from the last unit of the conveyor train and delivers this material to a discharge conveyor.
In the past, the mining machine utilized in the highwall mining system has comprised a continuous miner of conventional design. Such a miner incorporates a gathering head including mechanically driven gathering arms or centripetal/centrifugal loading arms that feed the coal rearwardly to a chain conveyor. Such a gathering arm mechanism has a number of distinct disadvantages.
First, it should be appreciated that each of the components necessary to operate and drive the gathering arms consumes vertical space and effectively functions to increase the height profile of the mining machine thereby limiting its operational capabilities to relatively thick seams where the necessary clearance is provided. Second, the gathering arms require their own drive motor, gearing and related electrical devices that significantly increase costs associated with both production and maintenance.
Third, due to their location (i.e. in a lowermost position beneath the head that cuts the coal from the seam and adjacent the ground or floor), the gathering arm gear cases are susceptible to infiltration by water and mud/sand/grit resulting in contamination and damage. This leads to significant downtime for repairs. Fourth, these components also consume a significant amount of the available horizontal and vertical space between the pan of the gathering head and the boom of the overlying mill or drum-type cutting head. In fact, the drive mechanisms for the gathering arms serve to create a narrow throat or bottleneck that disadvantageously slows conveyance of won aggregate material and thereby limits conveyor system through-put or carrying capacity.
Fifth, because of the space required to accommodate the gathering arm drive mechanisms, the conveyor system must be positioned relatively rearwardly. Thus, the distance that the cut aggregate material must be moved for deposit into the conveyor is increased. This requires the provision of greater "storage capacity" in the gathering pan to accommodate the aggregate material during transfer and necessitates additional work from the arms resulting in a broken product and the production of unwanted fines and a loss of production. Sixth, because of the expense of providing a drive mechanism for the gathering arms, the conveyor is normally driven by the same drive. Thus, the loaded conveyor is pushed from the front end (i.e. the load is conveyed by the slack side of the chain). This reduces conveyor efficiency and, unfortunately adversely affects overall conveyor service life. Recognizing these shortcomings, a need is identified for a mining machine of improved design particularly adapted for utilization in a highwall mining system.